Current treatment of solid tumors is limited by inherent tumor resistance to radiation or chemotherapy and toxicity from systemic administration of antineoplastic agents. Our long term goal is to overcome these limitations by developing a targeted therapeutic approach for localized tumors that increases the specificity and efficacy of the therapy and reduces the cytotoxicity in normal tissues. The c-Myc proto-oncogene is a transcription factor which plays a central role in the regulation of cell growth and differentiation, and its aberrant overexpression is associated with carcinogenesis. We have developed a thermally responsive polypeptide which inhibits c-Myc transcriptional activity and proliferation of cells in culture. Our hypothesis is that after systemic administration, genetically engineered polypeptides can be targeted to the tumor site by applying local hyperthermia. This will results in accumulation of the agent in the tumor with subsequent inhibition of tumor growth. The amino acid sequence of the designed polypeptides is based on elastin-like (ELP) biopolymers which are soluble in aqueous solution below physiological temperature 37 degrees C, but aggregate when the temperature is raised above 41 degrees C. A cell-penetrating peptide (CPP) is conjugated to the ELP to facilitate cell entry. To the CPP-ELP is added a peptide from the helix-loop-helix region of c-Myc, called H1, which inhibits the c-Myc pathway. Our preliminary in vitro results demonstrate a very significant effect of the CPP- ELP-H1 construct in MCF7 cells when compared to a non-thermally responsive control peptide. In order to address the hypothesis, the following specific aims will be addressed: (1) Create a suitable animal model to test the hypothesis in vivo through implantation of the MCF7 cells in the thigh muscle of athymic rats, (2) Measure the plasma kinetics and in vivo distribution of CPP-ELP-H1 in normal and neoplastic tissue in an athymic rat model by determining the plasma concentration curve and determination of the tissue concentrations with quantitative autoradiography.and (3) Evaluate therapeutic efficacy of CPP-ELP-H1 in the treatment of neoplastic xenografts in the thigh of athymic rats with and without localized hyperthermia through repeated administration of the agent coupled with local hyperthermia. These studies will provide the basis for a new technology for targeted delivery of specific oncogene inhibitors. Specific targeting of the proposed therapeutic polypeptides to solid tumors by local hyperthermia would increase specificity and efficacy of treatment and reduce the cytotoxicity in normal tissues. Thus, development of the proposed polypeptide-mediated therapeutic delivery system would provide an alternative means to effectively substitute or augment present therapy for treatment of localized tumors. The successful completion of the proposed research will provide In vivo data to move this therapy towards the translational stage of human therapeutics. [unreadable] [unreadable] [unreadable] [unreadable]